If you’ve never subscribed to Google Play Music Unlimited, you can get a four month free trial right now, complete with a free YouTube Red membership, which gives you access to some exclusive content and (much more importantly) eliminates ads from YouTube videos.
You’ll need a credit card to access the trial, as it’ll automatically charge you after the four months are over, but you can cancel your account immediately, and still have access until the trial expires. Unfortunately, this promotion is only available for new Google Play Music Unlimited members - if you’ve ever had an Unlimited account in the past, you aren’t eligible.